1. Field of the Invention
The present invention relates to a dosing device for bulk material with a batch weighing scale attached to an outlet opening of a bulk material container. The invention also relates to a method for operating the dosing device.
2. Description of the Background Art
A dosing device with a batch weighing scale attached to an outlet of a container is known from WO 2009/065524 A1, which corresponds to US2011035048, and which is incorporated herein by reference. This batch weighing scale essentially comprises a horizontally extending conveyor that preferably can be a screw conveyor, and that is supported by a number of bearing devices on a fixed supporting framework. Provided between the supporting framework and the conveyor are a number of measuring devices that are arranged and designed so as to continuously sense the weight of the bulk material being conveyed by the conveyor. The conveyor is motor driven and is designed to convey the relevant bulk material in the prescribed direction from a receiving area to a discharge area.
Attached to the floor of the container is a vertical filling tube, which is routed to the receiving area of the conveyor. The container stores at least a portion of the bulk material to be conveyed, and, in cooperation with the filling tube, forms a feeder for the conveyor. An agitator may be provided in the container, by which means bulk materials, for example those which flow poorly, can be agitated, so that it is possible to ensure a mass flow in the container for uniform loading of the conveyor.
The container, or the filling tube attached to its floor, and the conveyor preferably are mechanically decoupled from one another in order to prevent motions that arise in the container from affecting the measurement results in weight sensing with the conveyor. In the case of a screw conveyor, decoupling is accomplished with a flexible collar, for example, that connects the filling tube of the container and a pipe fitting at the receiving area of the conveyor.
WO 2009/065524 A1 proposes a fully floating support of the conveyor so that exclusively the weight of an applicable conveyor is sensed in the continuous measurement. To this end, the conveyor is supported on the bottom by a number of self-aligning bearings on the supporting framework, wherein at least one self-aligning bearing has an integrated force transducer. The self-aligning bearings are located at each of the two ends of the essentially horizontal conveyor. In the conveying operation, the vertically flowing bulk material is redirected in a horizontal direction by the conveyor and is removed from the conveyor's receiving area.
However, in the conventional art, improvement is needed in that, especially for bulk materials with poor flow properties, extremely varying vertical forces can be caused by the continuing vertical flow of bulk material. These forces can be transmitted through the bulk material to the conveyor and thereby to the self-aligning bearings that are located under the conveyor at the receiving area. These forces can result in distortion of the measured values in weight sensing.